Since SAS has been mentioned, I would like to submit that's an apple-orange discussion. It doesn't apply to the gentleman's question, which regarded rear-engined, presumably air-cooled cars. SAS is in its own league, doing incredibly interesting things with an entirely different platform and experimenting with all kinds of things which sometimes don't make it to production cars. They've been beat up enough here, IMHO, and produce a stellar product for those patient enough to benefit.
Apart from that, I would STRONGLY encourage attending the proposed Mid-American gathering the Michiana and Illiconsin guys have been kicking around. It should be well-attended, if they can get something off the ground, with a few of just about everything within a day's drive.
My observations, for what little they'd be worth, are that the Beck is hugely solid, fairly bullet-proof and finished very nicely. They do bear a great resemblance to the originals, but also can be made to incorporate surprising amount of innovative technology at the Bremen facility.
The only drawback I see to the Beck is the height of the seats from the floor. I hadn't thought about that until I had a conversation recently with another Speedster owner -- then I started looking at pictures. If you're a taller person, you might think you're a little taller in a Beck than in someone else's car.
Vintage makes a really good product also. I really like them, and -- again, just my two cents -- they're really FUN to drive and easy to maintain. They are a really neat adaptation of old-school tech and looks in a true-to-form, simple to operate car.
I'm not on the fence, though. I'm a horsepower guy. I like the offerings of a giant engine and tube chassis for my driving habits. I would utterly destroy a Vintage in about a minute. A Beck might take a little longer, but I'd probably fare a touch better in the eventual crash.
Both companies have way over-the-top customer service, and the hobby is lucky to have them supplying cars to the unwashed masses for what really is a reasonable cost of entry into the game.
Whichever you decide on, if you're limited to those two choices, buy the best example for your needs. Don't jump on the first one that comes along.